1. Field of the Invention
This invention relates to a photographing apparatus for photographing contents for effecting the three-dimensional display of a transmission projection image (transmission image), and further to a three-dimensional image generating apparatus for generating the three-dimensional image of the transmission image.
2. Description of the Related Art
X-ray image (transmission image) photographing is generally carried out in health screening, group medical examination, etc. in medical treatment organizations. In recent years, there has been proposed a technique of not simply photographing a transmission image, but photographing an object to be observed from the entire circumference thereof, reconstructing a plurality of photographed transmission images to thereby obtain three-dimensional voxel data, and displaying a tomographic image in any slice plane by the use of an image rendering technique.
Now, as regards the former transmission image, a transmission image having directly photographed an object to be observed can be used for medical diagnosis or the like and therefore, an image of high spatial resolution can be obtained. On the other hand, because of being a transmission image, all kinds of information of a region of the object to be observed through which a radioactive ray has been transmitted are superimposed upon one another. Therefore, from the transmission image, it is difficult to accurately grasp the distribution of a particular region (sick region) on a three-dimensional space.
Also, by displaying a tomographic image in any slice surface by the use of the latter transmission image, it is possible to easily grasp the position of the particular region on the three-dimensional space. However, there is the problem that artifact (noise) gets mixed during the reconstruction of the transmission image, and as compared with the resolution of the photographed transmission image, the resolution of the reconstructed transmission image is reduced.
So, stereoscopic observation is being reconsidered as a technique having both of these. This stereoscopic observation is to directly observe a transmission projection image and therefore has the advantage that it can observe an image of high resolution and that it is easy to grasp the stereoscopic depth disposition of a region to be observed such as a particular region by stereoscopic vision using a parallax.
As a photographing method which can be applied to the photographing of such a stereoscopic observation image, there has been a three-dimensional type radioactive ray image pickup method described in Japanese Patent Application Laid-Open No. 2000-287958 (paragraphs (0004) to (0008), FIG. 1) (corresponding U.S. Pat. No. 6,256,372). This image pickup method using a radioactive ray source is such that the radioactive ray source is moved in a predetermined plane, and the position and radiation direction thereof are adjusted to thereby photograph a plurality of view point images (images from a plurality of different view points) used for time-sharing stereoscopic observation. Then, photographed two images are stereoscopically viewed, whereby a three-dimensional image can be observed.
However, there are individual differences in the degree of ease with which an image is directly stereoscopically viewed and therefore, it is desirable to effect stereoscopic vision by the use of a three-dimensional display device (such as a lenticular lens or a barrier parallax lens) (see “New Breast X-ray Photographing Method Using Three-Dimensional Display” by Natsuko Bandai, Central District Sectional Meeting, Japan Radioactive Ray Technical Society, Central District Sectional Meeting Journal Vol. 3, No. 1, 2001).
Description will hereinafter be made of the prior art using multi-eye three-dimensional display. FIG. 6A of the accompanying drawings shows the disposition relationship of three-dimensional image observation. The reference numeral 301 designates the light receiving surface of a transmission image photographing apparatus, the reference numeral 302 denotes an object to be photographed (object to be observed), and the reference numerals 3031 to 3035 designate radioactive ray sources or the light emitting position thereof. A view point 601 is indicative of the disposition relationship of the view point (in the positional relationship with the photographing apparatus) when a transmission image photographed by the light receiving surface 301 is displayed and observed on a display device. The reference numeral 602 denotes an image obtained when the transmission image photographed in such a disposition relationship as shown in FIG. 6A is displayed.
For example, for three-dimensional image display on a three-dimensional display capable of displaying only a horizontal parallax, radioactive ray sources are moved horizontally relative to an image pickup surface, and a three-dimensional image is displayed by the use of a plurality of images having photographed the transmission image at a plurality of radioactive ray source positions. In this prior art, the object to be photographed 302 is disposed between the radioactive ray source 3031 and the light receiving surface 301, and the radioactive ray source is caused to emit light, whereby the transmission image is photographed on the light receiving surface 301. Then, as shown in FIG. 6A, the transmission image obtained in such a disposition relationship that it is looked at from the opposite side of the radioactive ray source 3031, etc. is observed.
However, when a transmission projection image (transmission image) is to be displayed on the three-dimensional display, if display corresponding to the simple disposition relationship of a three-dimensional image is effected, that is, a photographed two-dimensional image is simply displayed in conformity with three-dimensional display, the recognition of the size and positional relationship of a region to be observed obtained from the three-dimensional image deviates from the positional relationship of the actual object due to the distortion peculiar to the transmission image different from an image by an image pickup apparatus such as a camera.
Particularly, three-dimensional display has as its object to assist the recognition of the depth disposition of a focus position, but due to the depth feature (such as the magnitude relation) of the transmission image by the distortion which usually differs from that by a camera, it is difficult to discriminate between the front surface and rear surface of the three-dimensional image still after three-dimensional display is effected. Thus, there has been a case where the front surface and the rear surface are reversely recognized.